The most commonly used solution nebulizers in atomic spectrometry include pneumatic nebulizers (PN), ultrasonic nebulizers (USN), and glass frit nebulizers (GFN). Most PNs are extremely inefficient because the majority of test solution, e.g., 98 to 99%, is directed to the drain. Glass frit nebulizers are highly efficient at low uptake rates, e.g., 50 to 150 uL/min. However, GFNs are disadvantageous because of the reduction in aerosol production as the result of repeated usage. For USNs, efficiency of aerosol production is improved by a factor of approximately 10 compared to PNs if the test solution is not highly viscous. However, the present commercial USNs are quite expensive compared to PNs and GFNs.
Conversion of ultrasonic humidifiers to low-cost ultrasonic nebulizers for plasma spectrometry has been described by Clifford et al and Qinhan et al. (Clifford, R. H. and Montaser, A., "A Low Cost Ultrasonic Nebulizer for Plasma Spectrometry", 16th Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies, Chicago, Ill., paper #320, October, (1989); and Qinhan, J., et al, Appl. Spectrosc. 183-186, (1990)). In principle, these nebulizers are similar in design to that developed by Wendt and Fassel (Wendt, R. H. and Fassel, V. A., Anal. Chem. 37, 920-922 (1965)) in that a transmitting bath was used to transfer the ultrasonic radiation to the test solution to be nebulized. Such devices are referred to as geyser-type ultrasonic nebulizers. Because these nebulizers were designed to be operated in a batch-type sampling mode, long-term precisions were not satisfactory due to gradual consumption of the test solution in the USN. Sample change-over was also time consuming.
Presently, there exists a need for an inexpensive continuous-type ultrasonic nebulizer suitable for analytical atomic spectrometry.